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Appendix VL


increasing the depth of the cut; and it will be noticed that this
advance occurs after every stroke, in whichever direction, being
adjusted from large to very small by the screw u, or put out of
action entirely. The traverse can also be stopped at will by
disengaging the stop h on the lever N, and the cut advanced by
hand. The headstock c can be swivelled on a central pivot and
bolted in any new position up to 90 from that shewn, thus per-
mitting the grinding of every variety of chucked work, cylindrical,
conical, or surfaced. The emery wheel x is supported in a head-
stock having two bearings that can be adjusted for wear by the
milled nuts at , for above all things these wheels must run truly
and without shake. The head is carried on a series of slides,
v/^, supported on the bracket w, the actual sliding taking place
between/ and q\ while v can be rotated regarding/, and q regard-
ing w. As indicated in the figure, the cut advance is across the
bed, but if the grinding head be turne4 round a vertical axis, not
only can any new position be maintained up to 90 from that
shewn, but the advance can be obtained in any given direction
depending on the relation of q to w. These changes are desirable
when coned work is to be ground as a part of long bars, which
would be outside the capabilities of the movements of c or L.
The pump^", driven from the pulley/on the first countershaft,
supplies water continuously to the wheel x through the pipe /,
which returns to the tank by pipe r; and wheel m is for hand
traverse when setting.

Internal grinding, that is the finishing of holes that have been
bored, requires a much higher rate of revolution for the emery
wheel, because of the very small diameter of the latter, and a
head for this purpose is shewn in Fig. 938. The headstock ,
for the work, is fastened to the table /, as already described, and
the work itself is supported in a concentric chuck /. The
grinding head a has two spindles, one of which, c, is for external
work. The right ward end of spindle c is provided with a pulley e
which drives the internal grinding spindle g through pulley /
The spindle , being revolved as usual by a vertical belt upon
pulley*?, serves, it will be seen, as an additional countershaft, and
causes the spindle g to revolve at the desired speed. The grinding
head in Fig. 935 is, therefore, adapted for internal grinding by